WW-5724 Hand out a clone of the cached MessageFormat - #1914
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AbstractLocalizedTextProvider caches MessageFormat instances by pattern and locale and returned the cached instance itself from buildMessageFormat. MessageFormat is not thread-safe, so concurrent callers rendering the same message formatted through one shared instance; with a date or time sub-format that produced output for the wrong argument or an exception. buildMessageFormat now returns a clone of the cached instance, so the cached entry is only ever a template and is never formatted directly. MessageFormat.clone() deep-copies the sub-formats. The pattern-parsing cache is kept; measured against a fresh instance per call and against synchronizing on the shared instance, cloning is the cheapest of the three. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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September 11, 2026 13:49
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Fixes WW-5724
AbstractLocalizedTextProvidercachesMessageFormatinstances by pattern and locale and returned the cached instance itself frombuildMessageFormat.MessageFormatis not thread-safe, so concurrent callers rendering the same message formatted through one shared instance; with a date or time sub-format that produced output for the wrong argument or an exception.buildMessageFormatnow returns a clone of the cached instance, so the cached entry is only ever a template and is never formatted directly.MessageFormat.clone()deep-copies the sub-formats. The pattern-parsing cache is kept.Two tests added to
StrutsLocalizedTextProviderTest: one asserts two lookups of the same pattern no longer return the same instance while the cache still holds one entry; the other renders a{0,date,short}message from four threads with distinct dates and asserts every output matches its own argument. Both failed before the change.Why clone rather than the alternatives: building a fresh instance per call drops the parsing cache the WW-5540 work relies on, and synchronizing on the shared instance serializes all rendering. Measured over 1.2M renders on JDK 17, cloning was the cheapest of the three (176 ms, against 409 ms fresh-per-call and 556 ms synchronized).
No configuration or API change. Applies to both maintenance lines; the 6.x backport follows.
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